A polarizer that can transmit and block light and a liquid crystal that can modulate light are the basic elements to comprise LCD. LCD application has shifted from calculators and watches in the early time to notebook computers, word processors, LCD projectors, LCD TV, automobile navigators and indoor and outdoor measurement equipment.
View angle is a very unique characteristic for LCD. As shown in FIG. 1 for a LCD panel, after the incident light from a backlight source 7 passes in sequence through a polarizer 6, a glass panel 5, an ITO conductive layer 3, a molecular orientation layer 2 and a liquid crystal layer 1, it illuminates by passing through a molecular orientation layer 2, an ITO conductive layer 3, a color filter 4, a glass panel 5 and a surface-treated polarizer 6. The output light has a specific orientation. That also means most output light from display is in perpendicular direction. If we watch a totally white screen from a very flat angle, we are very likely to see black color or lose color fidelity. Such effect may be usefull under some circumstances, but is undesirable for most applications. Therefore, LCD industry has strived to improve view angle characteristic for LCD.
Further, the LCD industry defines maximum view angle as the view angle to obtain contrast 10:1 (usually in four directions up/down/left/right). Contrast is defined as the ratio of bright-state transmittance (totally white) and dark-state transmittance (totally black). The higher the ratio is, the better the display is. Contrast issue does not exist in CRT display because a CRT display can easily present totally black screen. However, this is very hard for a LCD. The backlight source 7 composed of cold cathode fluorescent lamp (CCFL) can not turn on and off quickly, so the backlight source is always kept on. To obtain a totally black screen, liquid crystal module has to block all the light from backlight source 7. But due to physical characteristics, these components can not meet the requirement and always present light leakage.
As shown in FIG. 2, a traditional polarizer with 6˜8 micrometer hardcoat layer (HC layer) is subject to optical measurement for contrast from down view angle. As shown in FIG. 3, a traditional polarizer with 6˜8 micrometer anti-static layer (AS layer) is subject to optical measurement for contrast from down view angle. From the figures, it is known that HC polarizer has a contrast 6.1, while AS polarizer has a contrast 7.0. From the area formed by the periphery at 270 degree of the contrast figure and a solid curve, it is known that the enclosed area by the HC layer and the AS layer can not reach a contrast above 10 due to dark-state light leakage. On the other hand, this affects the display characteristic for LCD and results in undesirable applicability.